Vacuum cleaner appliances capable of picking up both wet and dry material, commonly referred to as wet/dry vacuums or wet/dry vacs, are well-known. Wet/dry vacs are often used in workshops and other environments where both wet and dry debris can accumulate.
Wet/dry vacs conventionally consist of a collection tank or canister, often mounted on wheels or casters, and a cover or lid upon which a motor and impeller assembly is mounted. The motor and impeller assembly creates a suction within the canister, such that debris and liquid are drawn in to the canister through an air inlet to which a flexible hose can be attached. A filter within the canister prevents incoming debris and liquid from escaping from the canister while allowing filtered air to escape. One example of a such a wet/dry vac is shown in U.S. Pat. No. 4,797,072.
A very substantial vacuum pressure can be created within the collection canister of a wet/dry vac. This is perhaps the primary reason why, in a majority of currently available wet/dry vacs, the collection canister is substantially cylindrical in its structural configuration. As is well known, such a cylindrical configuration is very capable of withstanding high vacuum pressure forces.
There are at least several reasons why cylindrically-configured collection canisters for wet/dry vacs may be less than ideal. From a functional standpoint, a cylindrical configuration is not conveniently scalable. That is, as the capacity or size of the collection canister is increased, the overall height of the appliance likewise must increase. This is undesirable for several reasons, including the fact that it makes the appliance inconvenient to store and to move around, and that it increases the height of the center of gravity and hence the instability of the appliance. (The problem of vertical instability of wet/dry vacs has been recognized in the prior art; see, e.g., U.S. Pat. No. 5,560,075 to Jankowski, entitled "Wet or Dry Vacuum With Low Center of Gravity".)
Other prior art examples of wet/dry vacuums include: U.S. Pat. No. 5,548,868 to Berfield et al., entitled "Pilot and Detent Apparatus for a Vacuum Device;" U.S. Pat. No. 5,535,500 to Stephens et al., entitled "Method for Manufacturing a Bucket for a Wet/Dry Vacuum;" U.S. Pat. No. 5,598,605 to Tomasiak, entitled "Wet/Dry Utility Vacuum with a Wheel Mount;" U.S. Pat. No. 5,555,600 to Corson, entitled "Non-Tipping Wet/Dry Vacuum;" U.S. Pat. No. 5,606,769 to Tomasiak, entitled "Wet/Dry Utility Vacuum Cleaner with Detachable Blower;" U.S. Pat. No. 5,608,945 to Crouser, et al., entitled "Wet/Dry Utility Vacuum Cleaner;" and U.S. Pat. No. 5,611,107 to Tomasiak et al., entitled "Latching Mechanism for Wet/Dry Utility Vacuum Cleaner with Detachable Blower." The above-noted Tomasiak '605, '769 and '107 patents are commonly assigned to the assignee of the present invention, and are hereby incorporated by reference herein in their respective entireties.
While cylindrical vacuum collection canisters have some perceived disadvantages, most presently commercially-available wet/dry vacs have cylindrical canisters. Perhaps the principal reason for this is that non-cylindrical vacuum canisters can require obtrusive or extraordinary means for preventing collapse under the very high vacuum pressures generated in wet/dry vac systems. Such means could include, for example, exceptionally wide canister rims, or structural ribs and stiffeners on the inside and/or outside of the canister, or very thick wall sections. Such features would be undesirable from the standpoints of manufacturability, aesthetics, and ergonomics. In addition, internal stiffening structures could adversely affect the pneumatic/hydraulic performance of the vacuum, and would make the canister more difficult to empty and clean.
Of course, a vacuum canister can be made sufficiently strong enough to withstand the vacuum forces to which it is to be subjected by using very strong materials. However, such materials, e.g., metal, can be expensive and heavy, and are less than ideal for this purpose. Instead, conventional wet/dry vac canisters are preferably made of injection-molded plastics or the like, which are reasonably strong at appropriate thicknesses, and advantageously inexpensive and light-weight. Again, while plastic canisters can be made sufficiently strong by increasing their thickness, it is desirable from the standpoint of manufacturing expense, weight, and so on, to make the canisters as thin-walled as possible.
For smaller capacity wet/dry vacs, e.g., 3-gallon vacs, for instance, the problem of potential canister collapse is not as great, making non-cylindrical canister configurations more feasible. One reason for this is that smaller capacity vacs tend to have smaller motors which generate lower levels of vacuum pressure. Also, smaller canisters can readily be made sturdy and resistant to collapse without undue increases in weight, size, manufacturing cost, and so on. For larger capacity vacs, e.g., 12- or 16-gallon canisters, however, the potential for non-cylindrical canister collapse is considerably greater, and the approaches to making the canisters resistant to collapse that can be taken for smaller vacs are not as feasible or effective in terms of size, weight, manufacturing cost, etc . . . .